Long Term Evolution (LTE) handheld communication devices continue to be developed with trends toward smaller devices and wider bandwidth operation. Size limitations of thin mobile devices present challenges for internal antenna design in LTE/2G/3G wideband operations. Operating a single device at different locations with distinct regionally-enforced communication standards presents additional challenges. This is clear from Table I, which illustrates possible LTE band distributions for the Evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (e-UTRA) radio access standard used in various geographical regions.
TABLE 1DuplexUplink Freq.Downlink Freq.e-UTRAModeRangeRangeBand IVFDD1710-1755 (MHz)2110-2155 (MHz)Band XIIIFDD777-787746-756Band XVIIFDD704-716734-746Band XXFDD832-862791-821Band XXXVIIITDD2570-2620Band XLTDD2300-2400
Slot antennas provide simple radiating structures for use in such mobile devices and various technologies for tuning slot antennas exist. For example, U.S. Pat. No. 7,176,842 entitled Dual Band Slot Antenna incorporates electronic components prudently distributed across the antenna slot to shunt the slot at certain locations, thereby changing the antenna's effective length. US Patent Application Publication 2005/0174294 entitled Switchable Slot Antenna discloses another technique by which the effective length of the antenna is changed by solid state shunt switches distributed across the slot antenna. Both of these techniques rely on the distribution of switches across the radiating slot, each of which requires its own control signals, e.g., bias voltages. The distributed nature of the tuning circuits of these antennas increases the size of the overall circuit. Moreover, both of the afore-referenced systems utilize a half-wavelength slot, which imposes mechanical limitations on the antenna and, thereby, on the size of the mobile device. The need for smaller tunable antennas for mobile communication devices continues to be felt.